This invention relates to an integrated system for converting methanol to high octane liquid fuels, such as hydrocarbons. In particular, it provides a continuous process for producing hydrocarbon fuel products or the like by converting the aliphatic oxygenate feedstock catalytically to an intermediate lower olefinic stream, etherifying C.sub.4.sup.+ tertiary olefins and alkylating isobutane or other isoparaffins with olefins to produce light distillate and/or gasoline products.
In order to provide an adequate supply of liquid hydrocarbons for use as synfuels or chemical feedstocks, various processes have been developed for converting coal and natural gas to gasoline and distillate. A substantial body of technology has grown to provide oxygenated intermediates, especially methanol. Large scale plants can convert methanol or similar aliphatic oxygenates to liquid fuels, especially gasoline. Demand for liquid hydrocarbons has led to the development of processes for making liquid fuels by various synfuel techniques.
Increasing demand for high octane gasolines blended with lower aliphatic alkyl ethers as octane boosters and supplementary fuels has created a significant demand for isoalkylethers, especially the C.sub.5 to C.sub.7 methyl alkyl ethers, such as methyl tertiary butyl ether (MTBE) and tertiary amyl methyl ether (TAME). Recently, it has been announced that a commercial plant produces mixed ethers from C.sub.4 -C.sub.7 tertiary olefins and methanol to increase FCC naphtha octane. It has been found advantageous to provide a methanol-based conversion unit which can produce the required intermediate chemicals.
Recent developments in zeolite catalysts and hydrocarbon conversion processes have created interest in utilizing olefins, for producing C.sub.7.sup.+ alkylate gasoline, etc. In addition to the basic work derived from ZSM-5 type zeolite catalysts, a number of discoveries have contributed to the development of new industrial processes.
The medium pore ZSM-5 type catalysts are useful for converting methanol (MEOH) and other lower aliphatic alcohols or corresponding ethers to lower olefins and also for oligomerizing olefins. Particular interest has been directed to a catalytic process for converting low cost methanol to valuable hydrocarbons rich in ethene and C.sub.3.sup.+ alkenes. Various processes are described in U.S. Pat. Nos. 3,894,107 (Butter, et al.), 3,928,483 (Chang, et al.), 4,025,571 (Lago), 4,423,274 (Daviduk, et al.), 4,433,189 (Young), and 4,543,435 (Gould and Tabak), incorporated herein by reference. It is generally known that the MTO process can be optimized to produce a major fraction of C.sub.2 -C.sub.5 olefins. Prior process proposals have included a separation section to recover ethene and other light gases from by-product water and heavier hydrocarbons.
It is known that isobutylene may be reacted with methanol over an acidic catalyst to provide methyl tertiary butyl ether (MTBE) and isoamylenes may be reacted with methanol over an acidic catalyst to produce tertiary amyl methyl ether (TAME). The catalyst employed is preferably an ion exchange resin in the hydrogen form. Substantially any acidic catalyst may be employed with varying degrees of success. That is, acidic solid catalysts may be used; such as, sulfonic resins, phosphoric acid modified kieselguhr, silica alumina and acid zeolites.
It has also been recently reported that higher tertiary olefins, typically found in FCC naphtha, may be converted over similar catalysts to mixed ethers. The feed may contain C.sub.4.sup.+ tertiary olefins, which will produce their respective ethers. A process called "Etherol" has been announced to convert mostly C.sub.4 -C.sub.7 tertiary olefins (C. P. Halsig, B. Schleppinghoff, and D. J. Westlake, "Erdoelchemie and BP Ether Technology--More Scope for Octane Boost" 1986 NPRA Annual Meeting, Mar. 23-25, 1986, Los Angeles, paper AM-86-64). A bifunctional catalyst to hydrogenate diolefins in the feed has also been disclosed (P. M. Lange, F. Martinola and S. Oeckl, "Use Bifunctional Catalysts for MTBE, TAME, and MBK", Hyd. Process. December 1985, 51-52).